Area Forecast Discussion
Issued by NWS Sacramento, CA
FXUS66 KSTO 140504
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
1000 PM PDT Sun Jul 13 2014
Hot temperatures will peak Monday followed by a slight cooling
trend into mid-week. A chance of Sierra crest thunderstorms Monday
south of Lake Tahoe, then thunderstorm chances spread north into
the northern mountains during mid-week.
Max temps on Sun were some 6-10 deg warmer over much of the CWA
except for the far Nrn zones where they were about 1-4 deg warmer.
The heat is forecast to peak on Mon as the warmer air aloft moves
into our CWA.
Strong high pressure centered over the Great Basin will continue to
build westward early this week. As it does, temperatures will peak
across the region on Monday as onshore flow diminishes and a very
warm airmass moves overhead NorCal (850 mb temperatures around
28C-30C). Maximum temperatures in the Central Valley are expected to
range from 100 to 110. Enough moisture may make it up into the
Sierra to around Lake Tahoe on Monday for a few late day
Deeper mid and upper-level moisture (around 3 standard deviations
above normal) makes it northward into the region on Tuesday and
Wednesday allowing the thunderstorm threat to shift northward into
the northern mountains and become more extensive over the northern
Sierra. There may be some disturbances embedded in the southeast
flow over the area during mid-week that will carry convection off
the mountains and continue activity overnight, but these likely
won`t be evident until 24-36 hours prior. There seems to be some
consensus in the modeling that there is a weak wave near the CA/AZ
border that will rotate NWwd on the Srn periphery of the Great Basin
high and out over the ocean on Mon. This makes the 8 ubs mid-level
(elevated) instability in the Sac Vly on the 14/00z GFS a bit
suspect. Certainly the SEly flow looks strong enough to spread the
monsoon moisture NWwd however. Another wave or possibly a convective
feedback gremlin from the desert SW convection may rotate NWwd Tue
afternoon and Tue nite. The flow however is much weaker as it is on
Wed while it begins to transition to more variable direction that
convection is likely to be focused along and E of the Siernev Crest.
Certainly no storms would translate/propagate into the foothills/
valley...they would have to develop...and given the weak synoptic
forcing that seems very problematic for our CWA.
The increase in clouds along with a return of the Delta Breeze
will bring a gradual moderation of temperatures beginning Tuesday.
Overnight low temperatures will also be mild given all the cloud
cover. Even though temps will "cool"...the increase in humidity may
make it "feel" more humid and uncomfortable. JHM/DFR
.Extended Discussion (Thursday through Sunday)...
Monsoonal moisture will remain over the area through at least
Thursday...bringing continued chances of thunderstorms across the
mountains. By Friday or Saturday, the upper level high pressure
will begin to shift eastward back toward the Four Corners region.
Upper level flow over NorCal will become more westerly accordingly,
ending the threat of thunderstorms across most of the mountains.
We`ll retain a slight chance of convection south of Lake Tahoe
into next weekend due to greater uncertainty.
Temperatures should remain within a few degrees of normal through
the extended period. Dang
Mainly VFR conditions the next 24 hours across interior NorCal.
Southwest winds 15-25 kt continue near the Delta, elsewise winds
to remain below 10kt. Dang